In recent years there has been active research in the area of generation of nanosecond type pulses utilizing a high power photoconductive solid state switch coupled to a storage device. In such systems, the photoconductive switch must exhibit a transition from a high resistivity state to a conductive state in a sub-nanosecond time interval. One such switch is disclosed in U.S. Pat. No. 5,028,971 issued to Anderson H. Kim et al on Jul. 2, 1991, and entitled, "High Power Photoconductor Bulk GaAs Switch" which is incorporated herein by reference. This patent discloses a photoconductive gallium arsenide (GaAs) switch having two mutually opposite gridded electrodes which receive activating light from a laser. When the laser light is applied to the switch, the electrical resistance of the semiconductive material is decreased through electron/hole pairs being generated. This resistance change is translated into a change in the current that flows through an output circuit. The other critical element in the generation of fast electrical pulses is the energy storage element. Depending on the desired structure, the energy storage element should not only produce sub-nanosecond pulsewidths, but also should provide voltage enhancement.
Heretofore, two general techniques have been used to generate and deliver fast rise time, high power pulses to a load impedance. The first technique utilizes the recombination property of the semiconductor material from which the switch itself is fabricated. The pulses generated with this technique using photoconductive GaAs switches typically have a long pulsewidth with a relatively long recovery time at high bias voltage. This long recovery time has been attributed to the substantially long recombination time and the switch lock-on phenomenon exhibited by gallium arsenide. The second technique controls the output pulsewidth by an energy storage element which comprises either a short section of transmission line or capacitor. This energy storage element is utilized to deliver all or substantially most of the stored energy to the impedance load so that only a closing photoconductive switch is required. Neither of these techniques, however, produce an ideal subnanosecond pulsewidth because of the extended recovery time inherent in most photoconductive switches.